Catálogo de publicaciones - libros

The UK Environment Agency currently maintains over 35,000 km of coastal and flood defence embankments in England and Wales with an annul expenditure of approximately £400m. The majority of the flood defences are earth embankments built from locally available materials using traditional construction methods. Although the performance of the flood defence embankment can be jeopardised by several different failure modes, instability due to the fine;l,,,lay fill has been identified as one of the main causes of failure especially along the eastern coast and Tha dfg mes Estuary. At these locations medium to highly plastic clays are commonly used as fill material. The fine fissuring of these clay fills can reduce the mass permeability of the embankment, leading to a rapid ingress of floodwater with catastrophic collapse of the inward face. As part of a wider research programme into the fine fissuring of clays, preliminary laboratory tests have been carried out into the formation of fissures for a variety of clays with different plasticities. The tests investigated an empirical relationship between the geometry of thin discs of soil with the onset of fissuring for different plastic indices.

Marly formations are widespread in Greece with major works founded on, or excavated in them. Perhaps the most spectacular of them is the Corinth Canal, a ca. 7 kilometre long canal with very steep (average inclination 4.5: 1) and Corinth marl. The excellent stability of the steep canal slopes has motivated extensive laboratory investigations of the mechanical properties of the Corinth marl at the Geotechnical Department of the National Technical University of Athens since several years, the latest of which involved the drying properties of the Corinth marls. The drying portion of the soil-water characteristic curve was determined from undisturbed block samples and from reconstituted samples re-consolidated to the in-situ stresses. The airentry pressure was found to be higher in the case of the undisturbed samples compared to the reconstituted/re-consolidated samples. Furthermore, the variation of the void ratio with suction up to the air-entry pressure was found to be close to the curve of void ratio versus effective stress from one-dimensional consolidation over the same stress range. This behaviour constitutes evidence of the validity of the effective stress principle up to the air-entry pressure. Finally, the paper concludes with estimations on the apparent cohesion change of the Corinth marl with suction.

Weather-related geo-hazards are a major concern for the railway industry m Canada. The financial losses that result from derailments and delays amount to millions of dollars every year. On the other hand, the assessment and management of geo-hazards is a difficult problem that involves complex coupled phenomena and numerous soil and weather parameters. The primary goal of this paper is to illustrate the manner whereby unsaturated soil mechanics can be taken from the soil property assessment level using techniques based on the soil-water characteristic curve (SWCC), to the solution of this real and highly complex problem. First, a concise description of the weather-related geo-hazards assessment model (W-GHA model) is given. Deterministic and probabilistic aspects of the model were developed within a Decision Analysis framework. The deterministic core of the model consists of a two-dimensional stability analysis combined with the analysis of the effects of weather conditions on the pore-water pressures. According to the proposed model, weather conditions interact with the ground through the flow of liquid water, water vapour, and heat. Critical embankment stability conditions are determined using a Dynamic Programming Method (DPM) combined with Finite Element based stress fields. The soil system is ultimately represented by a series of partial differential equations (PDE’s) governing conservation of mass and momentum. A discrete stochastic analysis is implemented within the proposed framework. Several unsaturated soil property functions are required as input to the system of PDE’s. The hydraulic conductivity (i.e., coefficient of permeability), vapour diffusion coefficient, thermal conductivity, volumetric specific heat, and shear strength are all nonlinear functions physically related to the SWCC. The methodology by which these soil property functions can be inter-related to the SWCC is presented. The theoretical model illustrates the manner whereby it is possible to quantitatively assess embankment stability based on weather conditions. The methodology is feasible and yet relatively comprehensive.

A fine-grained slope that exhibits slow movement rates was investigated to understand the mechanisms which lead to a consecutive development of mass movements in the Vorarlberg Alps (Austria). For that purpose intensive hydro-meteorological, hydro geological and geotechnical observations as well as survey of surface movement rates were conducted from 1998 –2001. Subsurface water dynamics at the creeping slope turned out to be dominated by a 3 dimensional pressure system. The pressure reaction is triggered by fast infiltration of surface water and subsequent lateral water flow in the south west part of the hillslope. The related pressure signal was shown to propagate further downhill, causing fast reactions of the piezometric head in 5.5 m depth on a daily time scale. The observed pressure reactions might belong to a temporary hillslope water body that extends further downhill. The related buoyancy forces could be one of the driving forces for the mass movement. A physically based hydrological model was adopted to model simultaneously surface and subsurface water dynamics including evapotranspiration and runoff production. It was possible to reproduce subsurface pressure reactions and observed runoff in principle. However, as soil hydraulic functions were only estimated on pedotransfer functions a quantitative comparison between observed and simulated subsurface dynamics is not feasible. Nevertheless, the results suggest that similar methods of coupling surface and subsurface processes should be employed in coupled models for large mass movement and that it is possible to reconstruct important spatial structures based on sparse observations in the field.

The paper deals with the stability of slopes under drawdown conditions taking into account the effect of negative pore-water pressures, usually neglected in routine analyses. A simplified unsaturated soil profile above the water table was assumed and soil suction was estmiated using a Brooks and Corey type soil-water characteristic curve. A parametric study was carried out to evaluate the influence of geometrical, physical and mechanical parameters of a simple slope. The results for complete and rapid drawdown conditions show that the factor of safety varies less than 10% for dams or reservoirs with initial drawdown ratios less than 0.3. Soil suction becomes more significant (safety factor variation up to 50%) for railway or road embankments with the water level at the base of the slope.

The papers presents a numerical analysis of the stability of a moraine slope that reactivated after two heavy rainfall events in November 2000. To analyse the pore water pressure distribution within the slope, rainfall and evapotranspiration were applied to the slope over a period of four years that preceded the main landslide reactivation. Because of the uncertainty about the saturated hydraulic conductivities of the landslide soils, different combinations of these coefficients were analysed. The factor of safety of the slope was then calculated at the time where the slope moved, as recorded by the inclinometer measurements. This made it possible to verify which combinations of saturated hydraulic conductivities were compatible with the slope movements.

Research on a bentonite-based engineered barrier for use in the safe underground disposal of high-level radioactive waste is a special multidisciplinary issue. In order to obtain findings enabling the design of such a construction, it is necessary to employ all the available experimental tools and procedures. With respect to the extremely long-term time requirements for the rheological stability and safety of the system as a whole, the results of long-term research have fully justified the use of physical modelling. The most relevant model types applied have been found to be those made at a scale of 1:1, referred to as Mock-Up models. A vertical model of a bench-scale buffer mass test of Czech smectitic clay in the KBS-3 modification (Swedish system) has been built at the Centre of Experimental Geotechnics, CTU, Prague. The model is fully instrumented, providing the continual multiparametrical measurement of all the relevant parameters. The whole experiment including the development of all the parameters measured can be seen on free-access dynamic web-sites (http://ceg.fsv.cvut.cz).

Since 1974, Belgium investigates the design for disposal of its High Level Radioactive Waste (HLW) in a deep clay formation, the “Boom Clay”. Although the clay formation is the main (natural) barrier against the transport of the radionuclides towards the biosphere, the design also involves several engineered barriers (multi-barrier principle). In the design developed in the late 1980’s, a non-saturated bentonite based material was chosen as part of this barrier system. Prior to demonstrating this design in conditions, a surface mock-up test has been operated between 1997 and 2002. This test served as a preliminary test on the performance of several components of the system, such as bentonite based backfill blocks and instrumentation. With clearly defined heating and hydration conditions, it gave us the opportunity to perform a large scale simulation of the hydration/saturation of the backfill at controlled conditions. After describing the general disposal design and the experimental set-up, this paper will detail the measurements and observations obtained during operating and dismantling the mock-up. To support the interpretation of these measurements and observations, a modelling of the experimental set-up is being performed. We further detail the characterisation programme carried out to obtain the input data for the modelling. Finally, lessons learned for the development of the design for the HLW disposal will be drawn.